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METHOD OF PREPARING A CHARGE O MATERIAL TO BE SINTERED April 7,' 193.1. J. E. GREENAWALT Fild. April 30, 1929 a r w W N A 5 m 0 i N5 Q FFN N M N A w 1.. W

"Patented Apr. 7, 1931 UNITED STATES PATENT OFFICE JOHN E. GREENAWALT. OF NEW YORK, N. Y.

METHOD OF PREPARING A CHARGE OF MATERIAL TO BE SINTERED Application filed April 30, 1929. Serial No, 359,374.

present practice, is then fed onto the grate of a sintering machine or onto a porous hearth placed upon the sintering machine grate, after which thesurface is ignited and suction applied to the charge to propagate the sintering action downwardly through the :0 charge.

The suction must be of suflicient intensity to draw air through the entire charge. and it often occurs in practice that, either through imperfect moistening or because of a weak spot in the charge, that the sintering may proceed more rapidly in spots and increase the velocity of the suction at this point, producing an imperfect sinter. In order to mitigate this evil, it has become the practice to feed the charge onto the sintering machine grate in two distinct layers, one of which,

the coarser, is laid directly onto the grate, while the layer of finer material is laid upon the coarser material. as described in Patent #1,610,424t granted December 14,1926. How ever, even the charging of the .material in two layers of different sized particleshas not entirely overcome the difliculty ofuniformly sintering a charge, as the material cannot be uniformly graded to a sufiicient extent to equalize the suction throughout the sintering charge.

Obviously, the causes of non-uniform sinter are the weak spots in the charge from which the material is displaced by the suction. and non-uniform passage of air through different points in the charge due to inequality in the amount of voids or spaces between the particles. I have found that by separating the material that is to 'be sintered into three or more components of graded sizes, and charging these components onto the grate 1n sucecession, the component of largest v size being placed next to the grate, I obtain a charge having practically uniform suction through- 5 out its entire extent. This is so from the fact that the voids increase downwardly from the top of thecharge and the increase in the resistance to the air passage caused by the superincumbent material is compensated for 0 by the increase in the voids below.

Bearing in mind this brief description, the following advantages of the invention will, be readily apparent 1. A uniform resistance is obtained throughout the entire area of the charge and a more uniform ignition is had because of the maximum drop in pressure on the top layer.

2. It is possible by this arrangement of the charge to treatcharges of greater total thickness than heretofore, thus increasing the capacity of a given machine. The grading of the material eliminates the smaller particles from the voids between the larger particles, thus lessening the resistance to the suction in the lower partof the charge. p

3. Should a weak spot occur in the charge,

'it will be restricted to the particular layer in which it occurs, and not extend entirely through the charge.

4. The finely crushed fuel will exist in a larger proportion in the layer of fine material at the top of the charge, facilitating ignition and providing the greatest heat where the greatest amount of sintering is to be done.

Other advantages of this method of charging the material will readily occur to those skilled in the sintering art from a perusal of the following description in connection with the drawing which represents more or so less diagrammatically, a sintering machine of the intermittent type, comprising a pan or holder and charge car for feeding the material thereto.

Referring to the drawings, 1 represents a sintering pan provided with the usual grate 2 for supporting the sintering charge, and hollow trunnions 3, 3 through which the suction is applied and upon which the pan is rotatable for dumping. A charge car C is provided with three hoppers 4, 5, and 6, in the present instance, as' there are to be three layers of material placed in the pan and each hopper contains material for one of the layers. The 'charge car travels over the pan in the direction of the arrow for charging, hence the front hopper 4 contains the material of largest size; the next hopper 5 contains the material of medium size and the last hopper 6 contains the finest material. The material that is to be sintered is of course crushed and moistened, and screened or graded for separating. into the required sizes that constitute the components of the charge which are placed in the respective hoppers 4, 5, and 6. The charge car C is then propelled by suitable mechanism (not shown) and as it passes over the pan the component of crushed material m is laid in a comparatively thin layer on the grate 2 of the pan, the component of the material of medium size m is laid on the layer m as the hopper 5 comes -1nto position over the pan,

and finally the component of fine material m" is discharged onto the layer m. All of the layers of material are charged into the pan with one passage of the charge car thereover; As the aggregate amount of coarser material constituting the charge is less than the aggregate amount of finer material the layers m and m" are somewhat thicker than the layer m.

It is obvious then, that the charge placed in the pan in a plurality of layers, such as just described, can be spread more evenly owing to the lesser volume of the feed stream than could a charge disposed into the pan as a single layer, as the larger quantity of material that is charged from the charge car would have a tendency tooverrun its bounds. In addition to the facility with which the pan may be charged when successive layers are superimposed. it is apparent that there is a minimum packing of material as it falls into the pan, so that the voids throughout the charge are at a maximum and there will be less total resistance to the passage of air through the charge. Then too, the segregation of the smaller particles from the larger prevents the smaller particles from settling into the voids between the larger particles,

thus preserving these voids.

It is customary in sintering operations to return for further treatment sintered material that is discharged from the pan in a finely divided condition, this material being fines are generally in a coarser condition than the fine 'unsintered material and when recharged into a sintering pan will constitute the bulk of the bottom layer; the next layer is then largely made up of return fines and unsintered material, while the top layer (m The return principally of unsintered material. The fuel which has been mixed with the ore will, of course, be in a very finely divided state and will therefore constitute a. greater part of the top layer than of the-layers below, so that the bottom layer will embody a comparatively small amount of fuel. This is as it should be, as the bottom layer will consist largely in the return fines and will require but a small amount of sintering. The top layer, which is practically all unsintered material, contains the largest amount of fuel which facilitates ignition and provides the greatest heat where it is required for sintering. As this top layer is sintered, its porosity of course is increased, thus lessening the resistance to the passage of air and causing the succeeding layers to sinter more rapidly and with a more uniform downward travel of the sintering zone.

Having described my invention, I claim:

1. The hereindescribed method of preparing a charge of materialto be sintered, which consists in segregating the material into three age of voids increasing from top to bottom of the charge.

2. The herein described method of preparing a charge of material to be sintered which consists in mixing with the finely divided material, fuel, and previously sintered material, arranging said mixture in a treating holder in a plurality of layers in a manner to preserve the voids therein, said top layer embodying the greatest proportion-of fuel and the smallest proportion of voids and the bottom layer embodying the greatest percentage of previously sintered material and the greatest percentage of voids. 3. The herein described method of preparing a charge of material to be sintered. which consists in mixing with the finely divided material, finely-divided fuel and previously sintered material, separating the mixture into three or more components according to the size of the particles, placing a layer of the component of largest sized particles intoa. treating holder, and successively placing layers of-components of diminishing size thereover so as to preserve the normal amount of voids in each layer,the, layer of smallest size constituting the top layer in the holder.

In testimony whereof I hereunto aflix my signature.

JOHN E. GREENAWALT.

the case of the three layer charge) consists 

